(1) Field of the Invention
The present invention relates to receiver circuits and methods of down converting RF (radio frequency) signals. The present invention also relates to means and methods of down converting RF signals by first converting a radio signal to an IF (intermediate frequency) with a mixer and sampling the signal with a discrete time mixer/sampler block.
(2) Description of the Related Art
Several methods of down converting RF signals are known in the related art, and include:                (1) Super-heterodyne conversion which uses one or more lower IF to eventually reach the base band.        (2) Direct Conversion which uses a LO (local oscillator) tuned at the center frequency of the desired radio channel to bring the RF signal directly to the base band.        (3) Direct Sampling which uses a sampler at a RF, a method equivalent to the use of a LO.        (4) Sub sampling which uses a sampler operating at relatively lower frequencies.        
A block diagram of a typical super heterodyne receiver is shown in FIG. 1. An RF signal arriving at an antenna 25 passes through a band filter 100, a low noise amplifier (LNA) 101 and into an image filter (IMG FLT) 102 which produces a band-limited RF signal that enters a first mixer 103 which transforms the RF signal down to an intermediate frequency (IF) by mixing the RF signal with the signal created by the first local oscillator (LO) 200. The IF then passes through an IF filter 104 where unwanted mixer signals are removed. The signal then passes into an in phase quadrature sampler (I.Q.) 106. A second LO 201 sends a frequency signal to an I.Q. 106. An I.Q. 106 produces a baseband output in phase at 507b and quadrature out at 507c. 
FIG. 2 is a block diagram of a direct sampling receiver, consider as prior art. FIGS. 1 and two are identical from antenna 25 to image filter 102. For the direct sampling receiver of FIG. 2, the output of IMG FLT 102 connects to a sampler 110. The output of a LO 200 connects to both a sampler 110 and a clock distribution 202.
The output of sampler 110 enters an input of a DTP/DSP 300. The output from a clock distribution 202 also enters an input of a DTP/DSP 300. The output of a DTP/DSP 300 is the baseband output at 507.
The related art fails to provide means or methods of further reducing the number of components used in RF down conversion.
There is a need in the art for means to reduce the number of IF filtering components while providing sufficient image and alias rejection.
The related art fails to provide support for the down conversion of several frequency bands by minimal modification to existing receiver circuits.
There is thus a need in the art for new receiver circuits and new methods of down conversion of RF signals that consume less power, produce less heat, and are more economical to manufacture.